Ilana is having a baby and it is only three and a half weeks since conception. At this stage, which central nervous system structure (s) will have begun to form?

Answer: Neural tube

Explanation: Central nervous system originates from ectoderm, neuroectoderm gives rise to neural tube, the primordia of brain and spinal cord. Neural tube is the embryonic structure, neural plate folds into neural tube is formed at the dorsal side of embryo.